The radio communication spectrums are precious natural resources. At present the radio communication spectrums are allocated in a fixed allocation scheme. Currently there have not been sufficient spectrum resources allocated to systems carrying a high amount of service bearer, whereas excessive spectrum resources have been occupied by some other systems carrying a low amount of service bearer. In order to satisfy the demand of the systems carrying a high amount of service bearer for the spectrum resources, the cognitive radio technology has emerged.
The concept of a cognitive system has been introduced to the cognitive radio technology, which is also referred to as spectrum sensing radio technology. For a radio communication spectrum allocated fixedly to an access system, the access system is an incumbent system. An access system using with the radio communication spectrum allocated to the incumbent system based upon the cognitive radio technology is a cognitive system.
The cognitive radio technology operates under such a principle that the cognitive system intelligently detects the current radio environment of the radio communication spectrum allocated to the incumbent system to thereby dynamically select an idle one of frequencies allocated to the incumbent system for communication under the premise that there no interference between the cognitive system and the incumbent system.
With the cognitive radio technology, the cognitive system maintains a list of back-up frequencies (also referred to as a list of candidate frequencies) and transmits the maintained list of back-up frequencies to a terminal accessing the cognitive system. Once the current operating frequency is unavailable, the base station of the cognitive system and the terminal accessing the cognitive system select one back-up frequency from the list of back-up frequencies and switch to the selected back-up frequency for reconnection. Preferably they switch to a back-up frequency ranked first in the list of back-up frequencies, and if the back-up frequency ranked first in the list of back-up frequencies is unavailable, then they switch to the one ranked next.
In the prior art, the cognitive system can not determine a back-up frequency with reference to the back-up frequencies of other cognitive systems so that neither the stability of the system can be ensured nor the performance of the system can be improved. Consequently the existing solution for determining the back-up frequency by the cognitive system remains to be further improved.